Process for preparing methacrylonitrile and acrylonitrile by catalytic ammoxidation of isobutylene and propylene



United States Patent PROCESS FOR PREPARING METHACRYLONI- TRILE ANDACRYLONITRILE BY CATA- LYTIC AMMOXIDATION 0F ISOBUTYLENE AND PROPYLENEJamal S. Eden, Akron, Ohio, assignor to The B. F. GoodgchkCompany, NewYork, N.Y., a corporation of New No Drawing. Filed Aug. 30, 1965, Ser.No. 483,795

9 Claims. (Cl. 260465.3)

ABSTRACT OF THE DISCLOSURE Propylene or isobutylene, ammonia and oxygenare' contacted at an elevated temperature with a catalyst containingmanganese molybdate, tellurium oxide and a manganese phosphate to formacrylonitrile or methacrylonitrile.

ratio of 100 MnMO 10-100 TeO and -5() of a manganese phosphate. Thecatalyst can also be designated 3S MUMOmTe MI12 20P2 20039 12Q, P bfiingin th form of a phosphate i.e. each P atom is attached to 3 to 4 oxygenatoms.

Nitriles have been prepared by ammoxidation of hydrocarbons especiallyfrom the normally gaseous hydrocarbons. However, prior catalysts andprocedures for ammoxidizing propylene or isobutylene to acrylonitrile ormethaerylonitrile have certain shortcomings. The catalysts either have avery short active life, or they convert only a portion of thehydrocarbon to the desired unsaturated nitrile per pass; they oxidizethe hydrocarbon excessively to form high porportions of carbon monoxideor carbon dioxide or both or they are not sufficiently selective, sothat the hydrocarbon molecule is attacked at both the olefinicunsaturation and at a methyl group and large amounts of HCN andacetonitrile are formed.

It is therefore unexpected to find a catalyst that will convert fromover 50 to as high as 100% per pass of a monoolefin containing 3 to 4carbon atoms to yield very high proportions of acrylonitrile ormethacrylonitrile. A further unexpected feature is the unusually longactive life of the catalyst.

The reactants The essential reactants are propylene or isobutylene,ammonia and an oxygen containing gas, which can be pure oxygen, oxygenenriched air or air without additional oxygen. For reasons of economy,air is the preferred oxygen containing reactant.

The addition of steam into the reactor along with the monoolefin,ammonia and an oxygen containing gas is desirable but not absolutelyessential. The function of steam is not clear, but it does seem toreduce the amount of carbon monoxide and dioxide in the effluent gases.

Other diluent gases can be used. Surprisingly, saturated hydrocarbonssuch as propane or butane are rather inert under the reactionconditions. Nitrogen, argon, krypton or other known inert gases can beused as diluents if desired but are not preferred because of the addedcost.

Patented July 9, 1968 The catalyst and its preparation There are severalmethods for the preparation of the catalyst, which can be supported orunsupported. It is possible to dissolve each of the starting ingredientsin water and combine them from the aqueous solutions or the ingredientscan be dry blended. Because of the more uniform blend obtained by thesolution procedure, it is preferred.

A general procedure for preparing a catalyst is to provide the requisiteamount of a manganese molybdate in water, a tellurium compound and amanganese salt in water. Add the requisite amount of phosphoric acid tothe manganese salt solution. Add the tellurium compound to the manganesemolybdate and then add the manganese salt-- phosphoric acid mixture tothe manganese mloybdate-.- tellurium mixture. The catalyst is then driedand baked at 400 C. for about 16 hours.

Supported catalysts can be prepared by adding an aqueous slurry of thesupport to the aqueous solution of catalyst or the aqueous catalystingredients can be added to the slurry of the support.

Alternately a slurry of the catalyst ingredients can be prepared inwater, then dried and baked. For supported catalysts the aqueous slurryof the catalyst ingredients can mix them thoroughly. The main difficultyis to obtain thorough blending and uniform particle size.

A specific procedure for making the catalysts is as follows:

(a) Slurry 1 mol of manganese molybdate in water. (b) Slurry 89.2 g. ofammonium tellurate in water.

'Dry the. mixture on a steam bath and bake for 16 hours at 400 C.Thereafter the catalyst is ground to a mesh size of 10-18 and sieved.For supported catalysts an aqueous slurry of the support can be added atthe catalyst ingredients orvice versa prior to drying and baking. 45

Among the suitable supports are silica, silica containing material suchas diatomaceous earth and kieselguhr, silicon carbide, clay, aluminumoxides and even carbon,

although the latter tends to be consumed during the reaction.

If the catalyst is to be supported the aqueous solution or slurry ofingredients can be added to an aqueous slurry of the support or viceversa, prior to drying. The procedure after drying is the same as thatalready described. Thus, to the aqueous catalyst ingredients 240 g. (1.2mols) of a 3035% aqueous colloidal dispersion of microspheroidal silica(Ludox H.S.) are added slowly with stirring. Stirring is continued forabout /a hour prior to drying. Another procedure is to add the mixturedescribed under (c) to the Ludox and then add the requisite amount ofTeO and M00 as a slurry. Also the ingredients can be added to the Ludoxindividually if desired.

Another method is to grind MnMoO Te0 and a manganese phosphate to theproper particle size and then thoroughly mix the dry powders. Themixture can be added to an aqueous slurry of a support or vice versa andthereafter dried and baked.

For fixed bed systems a 10-18 mesh (U.S. Sieve) size is satisfactory.For fluid bed systems the catalyst particle size should be -325 mesh(U.S. Sieve).

The exact chemical structure of the catalyst made by the aboveprocedures is not known, but catalysts with molar ratios of IOO'MnMo,10-100 Te and 5:100 of a manganese phosphate can be used for convertingthe monoolefinic hydrocarbon to a nitrile. The catalyst containschemically bound oxygen so that the generic formula can be written asThe phosphate can be a P0,, radical, pyrophosphate or a polyphosphate,for example, manganese orthophosphate (ous), pyrophosphate, monohydrogenorthophosphate (ous) and dihydrogen orthophosphate (ous), andmetaphosphate (ic).

A preferred catalyst is one having a ratio of about 100 MnMoO 33 TeO and1030 Mn P O because it gives a high yield of desired products, and thepreferred support is silica, because of its low cost and good fluidizingcharacteristics.

Reaction conditions The reaction can be carried out in either a fixed orfluidized catalyst bed.

The reaction temperature can range from about 350 to 500 C. but thepreferred range is from about 375 to about 450 C. Below about 375 C. theconversion of monoolefin per pass and yield of unsaturated nitrile islower. Usually, a longer contact time is needed at lower temperatures toobtain the yields of unsaturated nitriles obtainable at temperatures inthe optimum range. Above 480 C. some of the acrylonitrile appears to beoxidized to carbon oxides, acetonitriles and HCN. This is much moreapparent at 500 C.

The mol ratio of oxygen to propylene should be from 1.5 to 1 andpreferably from 2 to 1 to 4 to 1 for good conversion and yields, butratios with some excess oxygen, 33 to 100% is even more desirable and ispreferred. There is no critical upper limit as to the amount of oxygen,but when air is used as the oxygen containing gas it becomes apparentthat too great an excess will require large reactors, pumping,compressing and other auxiliary equipment for any given amount ofdesired end product. It is therefore best to limit the amount of air toprovide 33 to 66% excess of oxygen. This range provides the largestproportion of nitrile under given reaction conditions. Also, since careis needed to avoid an explosive mixture the limiting of air aids in thatdirection. The mol ratio of ammonia to propylene can range from about0.5 to 1 to about 1.75 to 1. The preferred ratio is 0.75 to 1.5 ofammonia per mol of propylene.

The molar ratio of steam to propylene can range from to about 7, butbest results are obtained with molar ratios of about 3 to 5 per mol ofpropylene and for this reason are preferred.

The contact time can vary considerably in the range of about 2 to 70seconds. Best results are obtained in a range of about 8 to 54 secondsand this range is preferred.

The particle size of catalyst for fixed bed and fluid bed systems hasalready been described.

The reaction can be run at atmospheric pressure, in a partial vacuum orunder induced pressure up to 5 0100 p.s.i. Atmospheric pressure ispreferred for fixed bed systems and a pressure of 1 to 50 p.s.i. forfluid bed reactions. Care is needed to operate at a pressure which isbelow the dew point pressure of the acrylonitrile or methacrylonitrileat the reaction temperature.

The example is intended to illustrate the invention but not to limit it.

EXAMPLE The catalyst in this example was prepared by the solutionprocedure described above. It contained a molar ratio of 100 MnM0O 33TeO and 165 Mn P O and was unsupported. A high silica glass (Vycor) tube12 inches long and 30 mm. in outer diameter was filled with 170 ml. ofthe catalyst. Three external electrically operated heating coils werewound on the reactor. One of the coils extended along the entire lengthof the reactor and each of the remaining coils extended about One halfthe length of the reactor. Outlet vapors were passed through a shortwater cooled condenser. Uncondensed gases were passed through a gaschromatograph (Perkin-Elmer Model 154D) and analyzed continuously. Theliquid condenser was weighed and then analyzed for its acrylonitrilecontent in the gas chromatograph.

Steam at a temperature of ZOO-250 C. was first passed into this fixedbed reactor. Then propylene and air were fed separately into the streamof Water vapor. The mixture passed through a pre-heater and entered threactor at a temperature of ZOO-250 C. The reactor was preheated toabout 300 C. before the gas feed was begun. The molar ratio of the feedwas 3 mols of oxygen (supplied as air) per mol of propylene, 4 mols ofwater per mol of propylene and mols of ammonia per mol of propylene. Thetemperature in the reactor was raised to about 400 C. and held at thistemperature during the run. The cold contact time was 48 seconds.

99.2 percent of the propylene Was consumed in the reactor to produce amol percent yield of 77.59 of acrylonitrile based on the propyleneconverted at a mol percent efficiency of 76-98. No acetonitrile could bedetected in the effluent gases. The run was repeated at 400 C., acontact time of 46 seconds, 4.2 mols of steam and 4 mols of oxygen.98.98% of the propylene was converted for a mol percent yield ofacrylonitrile of 82.89 and a mol percent efficiency of 82.04.

The hydrocarbons which are ammoxidized according to this invention havethe formula The desired end products result from the ammoxidation ofonly one methyl group on the hydrocarbon molecule, while the terminal CH=C group remains intact.

The nitriles produced can be defined as alpha, beta monoolefinicallyunsaturated nitriles having 3 to 4 carbon atoms and a terminal CH =Cgroup or they can be defined by the general formula H (CHM-z CH:: -CN: Iclaim: 1. A method of producing compounds of the formula H (CII7)OICI{::C-CN

comprising, passing a mixture of a molecular oxygen containing gas in aquantity sufficient to provide a molar ratio of from about 1.5 to about4 mols of oxygen per mol of a hydrocarbon of the formula C 113- C H:

one mol of said hydrocarbon, and from about 1 to 1.75 mols of ammoniaper mol of said hydrocarbon, over a catalyst consisting essentially of amixture of manganese molybdate, tellurium oxide and a manganesephosphate in a molar ratio of 100 manganese molybdate, 10-100 itelluriumoxide and 5-50 of a manganese phosphate at a temperature of from about375 to about 500 C. at a contact time of from about 2 to seconds.

2. The method of claim 1 in which the hydrocarbon is propylene and thetemperature ranges from about 375 to about 475 C. to thereby produceacrylonitrile.

3. A method of preparing acrylonitrile comprising passing a mixturecontaining a molar ratio of one mol of propylene, sufficient molecularoxygen containing gas to provide from about 2 to about 4 mols of oxygenper mol of propylene, from up to about 7 mols of water vapor per mol ofpropylene and from about 1 to about 1.5

mols of ammonia per mol of propylene over a catalyst consistingessentially of a mixture of MnMoO Te and MIlzPgOq in a molar ratio of100 MnMoO 10-100 TeO and 10-100 Mango at a temperature of from about 400to about 480 C. with a contact time of 8 to 54 seconds.

4. A method of preparing :acrylonitrile comprising passing a mixture ofabout 3 to 4 mols of oxygen supplied as air, about 3 to 5 mols of watervapor and about 1 to 1.3 mols of ammonia per mol of propylene through abed of a catalyst consisting essentially of a mixture of MnM00 TeO andMn P O in a molar ratio of about 100 MnMoO 33Te0 and 10-30 MIlgPzOq at atemperature of about 375 to 425 C. and a cold contact tim of about 40-50seconds.

5. The method of claim 1 in which the catalyst is in -a fixed bed.

6. The method of claim 1 in which the catalyst is impregnated on asilicic support.

7. A method of preparing methacrylonitrile comprising passing a mixturecontaining a molar ratio of one mol of isobutylene, a molecular oxygencontaining gas in a quantity sufficient to provide from about 2 to about4 mols of oxygen per mol of isobutylene, up to 5 mols of water vapor andfrom 1 to 1.75 mols of ammonia per mol of isobutylene, through acatalyst consisting essentially of a mixture of MnMoO TeO and a MHzPgDqin a molar ratio of 100 MnMoO 10=100 TcO and 10-100 MIlgPgO'] at a[temperature of from about 400500 C. and a contact time of from about 2to about seconds.

8. The method of claim 7 in which the catalyst has a molar ratio ofMnM0O 33 Te0 and 10-30 M112P2O'7.

9. The method of claim 3 wherein the catalyst contains a majorproportion of manganese molybdate and lesser proportions of telluriumoxide and manganese pyrophosphate.

References Cited UNITED STATES PATENTS 3,228,890 1/1966 Eden 260-4653 XJOSEPH P. BRUST, Primary Examiner.

Patent No. 3,392,188

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION July 9, 1968 JamalS. Eden It is certified that error appears in the above identifiedpatent and that said Letters Patent are hereby corrected as shown below:

Column 3, line 70, "165" should read 16.5

Signed and sealed this 16th day of December 1969.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer

